1. Field of the Invention
The present invention relates to improved means for continuous filtration and, more particularly, to improvements in continuous filtering devices of the type employing endless belts of filter medium.
2. State of the Art
Filtration machines which employ endless belts of thin filter medium trained to travel over a drainage surface are well known for separating solids from liquids or slurries. One example of such a filtration machine is a rotary drum vacuum-type filter; another example is a pressure filter type of machine such as taught in my U.S. Pat. No. 3,760,945. In such filtration machines, it is requisite that the edges of the filter medium belt be kept parallel and aligned with the edges of the drainage surface to prevent vacuum from being lost and/or to prevent solids from entering the filtrate system. Another way of stating this requirement is that the filter medium belt must, within limits, be kept centered during its travel across the drainage surface. It is also requisite that the belt of filter medium be kept stretched laterally across the drainage surface; if this requirement is not met, wrinkles can develop in the belt which will interfere with the filtration operation as mentioned above and with the discharge of filtered solids from the belt.
Various devices have been proposed and utilized for aligning an endless belt of thin filter medium trained to travel across a drainage surface. Generally speaking, such devices have adequately accomplished the function of keeping the edges of a filter belt in parallel alignment, but have failed to satisfactorily prevent wrinkles from developing across the belt. As a rule, such prior devices have operated by slidably gripping beads which are sewn or otherwise affixed along the opposite edges of a filter belt; the beads function like a track which is moved and guided by the aligning devices. The beads add to the initial cost of the filter belts and also to maintenance costs because the beads wear due to the bearing pressure of the guide devices.
A primary object of the present invention is to provide, in combination with a filtering machine having an endless belt of thin filter medium trained to travel across a drainage surface to which vacuum or pressure is applied to separate liquid from solids or slurry carried by the belt, improved means for guiding and dewrinkling the belt of filter medium as the same travels over a drainage surface. A specific advantage of the device of the present invention is that it aligns and dewrinkles an endless traveling belt of thin filter medium without the belt being provided with a bead on either of its edges. The term "filtration machine" as utilized herein refers to devices for mechanically separating solids from liquids or slurries and includes the aforementioned vacuum and pressure type filters as well as pulp washers and the like which employ traveling webs of filter medium.
Further objects and advantages of the present invention may be readily ascertained by reference to the following detailed description and appended drawings, which are offered by way of example only and not in limitation of the invention, the scope of which is defined by the appended claims and equivalents.